Masteries

Offense:
20

Defense:
0

Utility:
10

Items

Doran's Ring: It will give you some health, mana regen and AP. With this item you will have more sustain in the lane.
Ninja Tabi: It will give you some armor at the begining. If the other team has too much AP you can change it for a Mercury's treads.
Randuin's Omen: It will make you a little bit more tanky and you will be able to initiate fights.
Rod of Ages: Will give you AP and a large amount of health. With these, the Randuin's Omen and the Ninja Tabi(or the Mercury's treads) you will be able of starting team fights and you will be a nice AoE tanky champ.
Rabadon's Deathcap: Essential if you want to deal tons of damage.
Void Staf: If you see other team is too tanky you can buy a Void Staf in order to have some magic penetration.
Lich Bane: It will give you some AP and mana. But the most important thing is that it will deal a very high amount of damage with "Takedown"(Q in cougar).